Well-known dental corrective techniques involve the replacement of a patient's teeth with artificial or false teeth. For example, a bridge is a type of dental corrective device which consists of one or more false teeth anchored between the patient's remaining teeth which abut the bridged site (known as "abutment teeth"), with the portion of the bridge that actually replaces the missing teeth being known as a pontic.
The bridge should be compatible with the patient's mouth in general and with the patient's other teeth to avoid discomfort and other problems. For example, when the teeth in a normal mouth are brought firmly together, the upper incisors (front teeth) should slightly overlap the lower incisors and the rest of the teeth should bite together with each upper tooth against its mate in the lower jaw and also against the lower tooth back of it. The bite is called occlusion. If the teeth do not bite together properly, the condition is called malocclusion and may interfere with masticatory movement (i.e., chewing) as well as with the symmetry of the face.
Rather than trial and error evaluation of a bridge in the patient's mouth, it is common to prepare a molded or cast dental model of both the upper and lower sets of teeth of the patient's mouth. The fit of the bridge is evaluated by use of the model and any necessary changes may be made to the bridge before installation of the bridge into the mouth of the patient. During evaluation of the bridge, it is desirable to study the compatibility of the bridge during both occlusal and masticatory movement of the dental model casts. To accomplish this, the dental model casts should be supported relative to one another in a manner which enables the simulation of the patient's mouth during occlusal and masticatory movement. Devices intended to provide such support are commonly known in the art as dental model articulators or correlators.
Known prior art articulators, particularly inexpensive ones, are disadvantageous in that they do not support dental model casts in a manner which approaches that of actual occlusal and masticatory movement of the jaw bone. Furthermore, because of the complex mouth movements which must be duplicated, many prior art articulators which are intended to more realistically reproduce mouth movement not only fall short of this goal but are complicated and expensive. Prior art articulators also are difficult to initially align and install on the dental model casts in a manner which duplicates the bite. This often results in poor alignment and reproduction of occlusion, and detrimentally affects reproduction of occlusal and masticulatory evaluation of the bridge.
Variations of an inexpensive disposable articulator currently in use for relatively simple restorations are disclosed in U.S. Pat. Nos. 4,382,787 and 4,449,930 to Huffman. These devices use ball-and-socket joint interconnections between mounts on the upper and lower dental models and a resiliently flexible, hinged bracket. The ball-and-socket joints pivotably interconnect the hinged bracket with the casts to enable the technician to manipulate the casts into their proper bite registry or perform other functions which require a pivotable interconnection between the casts and their connected brackets. After the desired positioning is achieved the ball-and-socket joints are immobilized with an adhesive.
However, devices of the type shown in the '787 and '930 patents suffer from the disadvantage that the bracket and mount configuration often does not provide sufficiently firm or uniform resistance to masticatory movements of the dental models. Also, the twisting force in the assembled model is concentrated at the relatively narrow neck of the ball spaced from the hinges and the model or on the long arms of the brackets, so that a considerable lever or torque force may be concentrated upon the neck or bracket which may lead to mechanical failure of the device. In addition, variations in the vertical spacing between the ball-and-socket joints due to variations in the thickness or vertical dimension of the model casts may cause the hinge axis to be shifted rearwardly or forwardly in relation to the casts, depending on the thickness of the casts. This results in an unnatural variation in the location of the hinge or pivot axis because the axis is actually brought closer to the teeth for larger or thicker casts, while in nature the reverse may actually be the case in that the jaw pivot point is generally spaced farther from the teeth when they are larger.